The following relates to the nuclear medical imaging arts. It particularly relates to head, neck, and brain scans performed using single-photon emission computed tomography (SPECT) cameras, and will be described with particular reference thereto. However, the following relates more generally to imaging of constricted anatomical regions such as the head, neck, or limbs using movable detector heads that follow trajectories closely conforming with the outer dimensions of the imaged anatomy.
In nuclear medical imaging techniques such as SPECT, a radiopharmaceutical is administered to the patient or other imaging subject. The radiopharmaceutical is typically designed to preferentially collect in an organ or tissue type of interest. For example, an intravenously administered radiopharmaceutical that remains in the blood system can be used to image patient vasculature, or the radiopharmaceutical can be designed to collect in preselected brain tissue to measure its metabolic activity, or so forth. For nuclear medical imaging, the radioactivity of the radiopharmaceutical is limited by permissible levels of patient radiation exposure. Accordingly, the level of radioactivity is typically low, and so the gamma detectors are of high sensitivity.
To improve detector sensitivity, the detector heads are typically positioned close to the anatomical region of interest. In tomographic imaging using detector heads that revolve around the imaging subject, the detector heads preferably orbit around the patient along a conformal path or trajectory that varies as a function of angular position to keep the detector heads close to the organ or region of interest without directly contacting the subject during the scan.
Many nuclear cameras are built with large gamma detector heads suitable for torso and body scans. Each gamma detector head typically includes: a honeycomb or other type of radiation collimator made of lead or another material with high radiation stopping power; scintillators that convert radiation to bursts of light; and photomultiplier tubes (PMTs), photodiodes, or other optical detectors for detecting the scintillation bursts. In some gamma cameras, each detector head has a radiation-sensitive area of about 40 cm×50 cm.
The combination of a close conformal path and relatively large-area detector heads can make tomographic SPECT imaging of constricted anatomical regions such as the head, neck, or limbs problematic. In the case of tomographic head or neck imaging, for example, the patient's shoulders can interfere with the detector head or with a mounting stricture supporting the detector head.
To improve conformity of the detector orbits with the external shape of the patient, it is known to use the detectors in an “asymmetrical” manner, in which an area of the detector face other than the geometrical center is aligned with the organ or region of interest. By aligning an edge region of the detector (e.g., 20 cm×20 cm) with the patient's head, for example, a closer positioning of the radiation detector head may be possible. In some approaches, data is collected using the entire detector face, and only data from the portion of the detector face yielding high counts is retained. However, this approach has been found to compromise image resolution. An improved approach defines a restricted “zoom” area of the gamma detector, and only the zoom area (e.g., 20 cm×20 cm) is used for collecting data.
These techniques are not wholly satisfactory for tomographic imaging of constricted anatomical regions. The off-center zoom area of the detector will often be optimal only for a limited portion of the conformal trajectory. In other trajectory portions, the choice of zoom may not be beneficial, and indeed may even be detrimental. Moreover, in the usual case where the SPECT camera includes two or more gamma detector heads, the zoom area of opposing detector heads should generally have aligned zoom areas. This imposes further compromises upon selection of the zoom area, since an optimal zoom area for one detector may be non-optimal for the opposing detector.
The following contemplates improved apparatuses and methods that overcome the aforementioned limitations and others.